The motor neuron diseases (MNDs) are a group of severe disorders that attack the brain and spinal cord.
They destroy motor neurons, which are the nerve cells that control muscles used for essential activities such as walking, speaking, swallowing and breathing.
Other famous sufferers of motor neuron disease include American baseball legend Lou Gehrig, for whom the most common MND, Lou Gehrig's Disease, is named; the brilliant British physicist Stephen Hawking; and screen star David Niven.
How MNDs affect the body
Normally, messages from nerve cells in the brain (called the upper motor neurons) are transmitted to nerve cells in the spinal cord (the lower motor neurons) and from there to specific muscles. Upper motor neurons direct the lower motor neurons to produce movements such as walking or chewing. Lower motor neurons control movement in the arms, legs, chest, face, throat and tongue.
MNDs disrupt the signals from the motor neurons to the muscles; the result can be gradual weakening and wasting away of muscle and uncontrollable twitching. When upper motor neurons are affected, there can be spasticity or stiffness of limb muscles and over-active tendon reflexes, causing knee and ankle jerks. Eventually, the ability to control voluntary movement can be lost.
Types of motor neuron disease
With Lou Gehrig's Disease, also called amyotrophic lateral sclerosis (ALS) or classical motor neuron disease, both upper and lower motor neurons are affected, and the disease eventually disrupts signals to all voluntary muscles. Symptoms usually first appear in the arms, legs or swallowing muscles. Affected individuals lose strength and the ability to move their limbs and body, and most have difficulty talking. The disease does not usually affect thinking or personality, although some people may have problems with decision-making and memory.
Most people with ALS die from respiratory failure, usually within 3 to 5 years; about 10 percent survive for 10 years or longer.
Some of the other more common MNDs include progressive bulbar palsy (affects motor neurons of the brain stem, causing slurred speech and difficulty chewing and swallowing); primary lateral sclerosis (affects the upper motor neurons); and progressive muscular atrophy (affects the lower motor neurons in the spinal cord). MNDs also include the inherited forms of spinal muscular atrophy and post-polio syndrome, a condition that can affect polio survivors decades after recovery from poliomyelitis.
Is there any treatment?
There is no cure or standard treatment for MND. Treatment is aimed at relieving symptoms to some extent and making patients more comfortable. The drug riluzole is used to treat Lou Gehrig's Disease, but it prolongs life by only a few months and does not help to relieve symptoms. Other medicines to reduce symptoms include muscle relaxants for spasticity, and drugs to relieve pain. Some patients require morphine to cope with musculoskeletal abnormalities or pain in advanced MND.
Physical, speech and occupational therapy may help improve posture, prevent joint immobility, slow muscle weakness and atrophy, and cope with swallowing difficulties. Assistive devices such as supports or braces, speech synthesisers and wheelchairs help some patients retain independence.
What is the prognosis?
Lou Gehrig's Disease and some forms of spinal muscular atrophy are fatal. There may be "plateau" phases where the conditions appear to be stable for a period, but degeneration will inevitably progress. Some MNDs, such as primary lateral sclerosis, are not fatal and progress slowly.
Who gets MNDs?
MNDs can occur in adults and children, and are more common in males. In adults, symptoms appear most often between 40 and 60 years. In children, particularly in inherited forms of the disease, symptoms can be present at birth or appear within the first year.
What causes MNDs?
Some kinds of MND are inherited, but in the majority of uninherited MND cases the cause is unknown. Some cases may possibly be triggered by cancers or chronic exposure to toxic drugs and environmental toxins, but this is very difficult to establish. Research is ongoing into whether the body's autoimmune response to certain viruses could trigger MNDs.
National Institute of Neurological Disorders and Stroke (NINDS). 2011. Fact Sheet: What are motor neuron diseases?
Motor Neuron Disease / ALS Association of South Africa